It is known to add a hydrazine compound to a silver halide photographic material or to a developer as disclosed in U.S. Pat. No. 3,730,727 (a developer containing a combination of ascorbic acid and hydrazine), U.S. Pat. No. 3,227,552 (hydrazine is used as an auxiliary developing agent for obtaining a direct positive color image), U.S. Pat. No. 3,386,831 (.beta.-mono-phenylhydrazine of an aliphatic carboxylic acid is contained as a stabilizer for a silver halide photographic material), and U.S. Pat. No. 2,419,975 and Mees, The Theory of Photographic Process, 3rd edition, page 281, (1966).
In particular, aforesaid U.S. Pat. No. 2,419,975 discloses a hard negative image obtained by the addition of a hydrazine compound. When a hydrazine compound is added to a silver chlorobromide emulsion layer and a photographic material having that emulsion layer is developed by a developer having a pH as high as 12.8, photographic characteristics having a very high contrast over 10 in gamma (.gamma.) are obtained.
However, since a high alkaline developer having pH near 13 is likely to be air-oxidized and unstable, such a developer is not fit for storage or use for a long period of time.
Super high contrast photographic characteristics over 10 in gamma are very useful for photographic reproduction of continuous tone images by dot images (which is useful for printing plate making), or for reproduction of line images. For this purpose, a process of using a silver chlorobromide photographic emulsion having a silver chloride content over 50 mol%, preferably over 75 mol%, and developing the emulsion layer with a hydroquinone developer having a very low effective concentration of a sulfite ion (usually less than 0.1 mol/liter) has hitherto been used. However, in this process, the developer is very unstable due to the low sulfite ion concentration in the developer and cannot endure storage over 3 days.
Furthermore, in these processes, since a silver chlorobromide emulsion having a relatively high silver chloride content is required, a high sensitivity cannot be obtained. Accordingly, there has been a strong demand for super high contrast photographic characteristics useful for the reproduction of dot images and line images using a silver halide emulsion having a high sensitivity and a stable developer.
In U.S. Pat. Nos. 4,224,401, 4,168,977, 4,243,739, 4,272,614 and 4,323,643, silver halide photographic emulsions giving very high contrast negative photographic characteristics using a stable developer are disclosed, but it has been found that the acylhydrazine compounds used in the techniques disclosed in the aforesaid patents have various disadvantages.
It is known that these hydrazines generate a nitrogen gas during development. These gases gather in a photographic film to form bubbles to reduce the photographic images, and further the gases enter processing solutions where they have a bad influence on other photographic light-sensitive materials being processed with such processing solutions.
As a means for preventing the nucleating agent from coming into processing solutions, it has been known to increase the molecular weight of the nucleating agent alone a conventional molecular weight to render the nucleating agent non-diffusible. But it has been found that the conventional nucleating agent thus rendered non-diffusible has the problem in stability of the silver halide emulsion containing the nucleating agent with the passage of time. That is, when the coating composition containing the nucleating agent is stored for a long time, the nucleating agent is deposited in the coating composition, which reduces the filtering property and further changes the photographic performances.
Also, when these conventional hydrazines are used, a large amount is required to increase contrast. Further, when a specifically high sensitivity in regard to the performance of the photographic light-sensitive material is required, and when other sensitizing techniques (for example, increasing the chemical sensitivity, increasing the grain sizes, and the addition of a compound of accelerating the sensitivity as described in U.S. Pat. Nos. 4,272,606 and 4,241,164) are employed together, sensitivity sometimes increases and fog resulting from that sensitivity increase occurs during the storage of the photographic light-sensitive material.
Accordingly, a compound which can reduce the generation of the aforesaid bubbles, which does not come into a developer, which does not cause the aforesaid problem with stability with the passage of time, and which can give very high contrast photographic characteristics with the addition of a very small amount thereof, has been desired.
Also, in U.S. Pat. Nos. 4,385,108, 4,269,929, and 4,243,739, it is disclosed that a very high contrast negative photographic character is obtained by using hydrazines having a substituent easily adsorbable to silver halide grains. However, in the hydrazine compounds having the aforesaid adsorbable group, the specific compounds described in the aforesaid patents have the problem of causing a desensitization during the storage of the photographic light-sensitive material with the passage of time. Accordingly, it is necessary to discover hydrazine compounds which do not cause these problems.
On the other hand, although there are various direct positive photographic processes, the process of developing a photographic light-sensitive material containing previously fogged silver halide grains after light-exposing the silver halide grains in the existence of a desensitizing agent and the process of light-exposing a silver halide emulsion layer having sensitive specks mainly in the inside of the silver halide grains and then developing the emulsion layer in the presence of a nucleating agent are most useful. The present invention belongs to the latter process.
A silver halide emulsion containing sensitive specks mainly in the inside of the silver halide grains and forming a latent image mainly in the inside of the silver halide grains is called an internal latent image type silver halide emulsion. It can be discriminated from a silver halide emulsion containing silver halide grains forming a latent image mainly on the surface of the silver halide grains.
A process of obtaining direct positive images by surface developing the internal latent image type silver halide emulsion in the presence of a nucleating agent and also the photographic emulsions and photographic light-sensitive materials which are used for the process are known.
In the aforesaid process of obtaining the direct positive images, a nucleating agent may exist in the developer. But when the nucleating agent is adsorbed on the surface of silver halide grains by incorporating the agent in a silver halide photographic emulsion layer or other suitable layer of a photographic light-sensitive material, better reversal characteristics can be obtained.
As a nucleating agent which is used for the aforesaid process of obtaining direct positive images, there are known hydrazines described in U.S. Pat. Nos. 2,563,785 and 2,588,982; hydrazide and hydrazine series compounds described in U.S. Pat. No. 3,227,552; heterocyclic quaternary salt compounds described in U.S. Patents 3,615,615, 3,719,494, 3,734,738, 4,094,683, and 4,115,122, British Patent 1,283,835, JP-A-52-3426, JP-A-52-69613 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"); thiourea bonded type acylphenylhydrazine series compounds described in U.S. Pat. Nos. 4,030,925, 4,031,127, 4,139,387, 4,245,037, 4,255,511, and 4,276,364 and in British Patent 2,012,443; compounds having a heterocyclic thioamide as an adsorbing group described in U.S. Pat. No. 4,080,207; phenylacylhydrazine compounds having a heterocyclic group having a mercapto group as an adsorbing group described in British Patent 2,011,397B; sensitizing dyes having a substituent having a nucleating action in the molecular structure described in U.S. Pat. No. 3,718,470; and hydrazine compounds described in JP-A-59-200230, JP-A-59-212828, and JP-A-59-212829, and Research Disclosure, No. 25310 (Nov., 1953).
However, it has been found that these nucleating agents for obtaining high contrast negative or positive images have insufficient nucleating activity. The nucleating agents having a high activity are insufficient in storage stability, and the activity thereof deviates after being added to a silver halide emulsion to coating. And when various kinds of nucleating agents are added, the quality of the emulsion layer is reduced.
For solving these faults, other nucleating agents are proposed in JP-A-60-179734, JP-A-61-170733, JP-A-61-270744, JP-A-62-65034, JP-A-62-948, JP-A-63-223744, JP-A-63-234244, JP-A-3-234245, JP-A-63-234246, JP-A-63-306438, and JP-A-1-10233, and European Patent Publication (unexamined) 345,025.
However, to lower pH of a developer for increasing the stability of the developer (i.e., preventing the deterioration of a developing agent), to shorten the processing time of development, or to reduce the reliance on changing of the developer (e.g., pH and sodium sulfite), nucleating agents having a more higher nucleating activity have been desired.